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Evans FT.
“The Effect of Several Psychotomimetic Drugs on Human Serum Cholinesterase”.
Psychopharmacologia. 1960;1(3):231-240.
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Abstract
Human serum cholinesterase (ChE) was inhibited almost to the same extent by LSD and the non- psychotomimetic BOL-148 (pI50 = 50 0nhibition produced by a dosage of 10-6.5M or 10-6M), and chlorpromazine which antagonizes the psychotomimetic effect of LSD was more effective (pI50 = 10-5M) than the psychotoomimetic Psilocybin (pI50 = 10-4.6M). Mescaline like amphetamine and meprobamate had no marked inhibitory effect. . Recently an "atypical" human serum ChE with varied affinity for certain ChE=inhibitor and substrates was described. Several drugs (but not Psilocybin) were tested against those atypical ChE (serum of patients with abnormal succinylcholine sensitiveness). All drugs inhibited the atypical ChE weaker than the typical, i.e. much weaker, except LSD and BOL-148. In the latter the difference was little and smaller than Kalow and Davies assumed for a ChE inhibitor with the point of reaction on the anionic site of ChE. According to them DFP and TEPP which react with esteratic site inhibit the typical and atypical ChE equally. Perhaps LSD and BOL-148 are reacting with both parts of ChE. . Inhibition of ChE was determined by a spectrophotographic method. The substrate was benzoylcholine. Regarding the discrepancies between psychotomimetic and anti-ChE effect the author remarks that other investigators using other assay systems, found a much lower anti-ChE activity of LSD. "Since the physiologic substrate of serum cholinesterase is not known, one can only conjecture which, if either, more accurately reflects the inhibition that obtains in vivo. Also, caution is necessary in attempting to extend these observations to the cholinesterase of other tissues, particularly of brain. Although Thompson et al obtained similar inhibition rates for brain and serum cholinesterase with LSD, as did Ord and Thompson with several other inhibitors, it is still not certain that the enzymes occurring in the two tissues are identical." . Comment: The following diagram from Cantarow and Scheparth shows the anionic and esteratic sites of the cholinesterase and its combination with ACh. The hypothesis of an attack at both the anionic and esteratic site has also been considered for prostigmin.
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